Islamist insurgents in Iraq have seized the city of Tikrit, their second major gain after capturing Mosul on Tuesday, security officials say.

Tikrit, the hometown of former leader Saddam Hussein, lies 150km (95 miles) north of the capital Baghdad.

Iraqi PM Nouri Maliki vowed to fight back against the jihadists and punish those in the security forces who fled offering little or no resistance.

The insurgents are from the Islamic State of Iraq and the Levant (ISIS).

ISIS, which is also known as ISIL, is an offshoot of al-Qaeda.

It controls considerable territory in eastern Syria and western and central Iraq, in a campaign to set up a Sunni militant enclave straddling the border.

There were also reports on Wednesday of fighting further south, in Samarra, 110km north of Baghdad.

Separately, at least 21 people were killed and 45 hurt by a suicide bomber at a Shia meeting in Baghdad, police said.

'Do not give in'

As many as 500,000 people fled Mosul after the militants attacked the city. The head of the Turkish mission in Mosul and almost 50 consulate staff are being held by the militants, Turkish officials say.

Turkey's foreign minister warned there would be "harsh retaliation" if any of its citizens were harmed.

Heavy fighting was reported in Tikrit as militants swept in

Militiamen consolidate their hold on Tikrit

The insurgents moved quickly south, entering the town of Baiji late on Tuesday.

There were heavy clashes reported in Tikrit, with dozens of insurgents attacking security forces near the headquarters of the Salaheddin provincial government in the city centre.

One eyewitness told the BBC that gunmen had entered the city from four different directions and a police station had been set on fire.

AFP news agency quoted police and witnesses as saying there was fighting at the northern entrance to Samarra.

Earlier Mr Maliki vowed to fight back against the militants. He has asked parliament to declare a state of emergency.

ISIS in Iraq

The Islamic State of Iraq and the Levant (ISIS) has 3,000 to 5,000 fighters, and grew out of an al-Qaeda-linked organisation in Iraq

ISIS has exploited the standoff between the Iraqi government and the minority Sunni Arab community, which complains that Shia PM Nouri Maliki is monopolising power

It has already taken over Ramadi and Falluja, but taking over Mosul is a far greater feat than anything the movement has achieved so far, and will send shockwaves throughout the region

The organisation is led by Abu Bakr al-Baghdadi - an obscure figure regarded as a battlefield commander and tactician. He was once the leader of al-Qaeda in Iraq, one of the groups that later became ISIS.

In a live TV address, he said a "conspiracy" had taken place in Mosul and surrounding Nineveh province.

Mr Maliki said he did not want to apportion blame for who had ordered the security personnel "to retreat and cause chaos".

He added: "Those who deserted and did not carry out their jobs properly should be punished."

Mr Maliki told the people of Nineveh: "Do not give in. We are with you, the state is with you, the army is with you. Even if the battle is a long one, we will not let you down."

Charities have expressed fears for the tens of thousands fleeing the advance

A suicide attack on a Shia gathering in Baghdad left dozens dead and injured

He pledged to "reorganise the armed forces to cleanse Nineveh of the terrorists".

The BBC's Jim Muir says people in Mosul are reporting that militants there have been travelling around the city telling them they are not in danger - even the Shia residents - and that people should go back to work.

ISIS has been informally controlling much of Nineveh for months, and in the past week has attacked other areas of western and northern Iraq, killing scores of people.

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PM Nouri Maliki blamed the fall of Mosul on a conspiracy

The US has condemned the militants, but BBC world affairs correspondent Paul Adams says the West's response is not going to be military, as there is no appetite to return to a battleground that claimed thousands of British and American lives.

UK Foreign Secretary William Hague said there was "no question" of British troops returning to Iraq, five years after they ended combat operations there.

He said that the Iraqi government had "considerable resources" and it was up to its armed forces to respond.

The Iraqi government is struggling with a surge in sectarian violence that killed almost 800 people, including 603 civilians, in May alone, according to the UN. Last year, more than 8,860 people died.

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